Dual fluid circulatory support system



Oct. 27, 1970 1-. c. ROBINSON ,536,

DUAL FLUID CIRCULATORY SUPPORT SYSTEM Filed Feb. 6, 1969 .5 Sheets-Sheet 1 L Mid/W310 ATTORNEYS F I G. 2 4

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DUAL FLUID CIRCULATORY SUPPORT SYSTEM Filed Feb. 6, 1969 5 sheets-sheet 2 FIG. 3

FROM VENTRICLE .r0 1

AORTA i i 2'5 INVENTOR.

- THOMAS c. ROBINSON 245 V 243 BY I Z4ML ATTORNEYS Oct. 27,1970 T. c. ROBINSON I 3,536,423

DUAL FLUID 'CIRCULATORY SUPPORT SYSTEM Filed Feb. 6, 1969 Sheets-Sheet 3 s7 '6"' 4 II II I; I I BLOOD I ENGINE I I IN 000 BL I g Q I I 97 I i I 9 I 3| as I 27 I (99 95 BLOOD PUMP I I I A H R i CONTROL UNIT P I 77 79 8| I 87 I W I I I 4 LPR 73 I L 2WE I FIG. 5

F I G. 8 I I INVENTOR. THOMAS c. ROBINSON BY ATTORNEYS O t- 7, 19 0 T. c. ROBINSON 3,536,423

DUAL FLUID CIRCULATORY SUPPORT SYSTEM Filed Feb. 6, 1969 5 Sheets-Sheet 4 INVENTOR. 7 THOMAS c. ROBINSON BY 6 w/ t- F l G M /4Zw :A..

' ATTORNEYS Oct. 27, 1970 T. c. ROBlNSON 3,5

DUAL FLUID CIRCULATORY SUPPORT SYSTEM 7 Filed Feb. 6, 1969 5 sneet sheets EXHAUST n I \J 9 TO SUMP PUMP 99,.

7 99 INVENTOR.

THOMAS c. ROBINSON Y 7 f F IG. 7

ATTORNEYS United States Patent 3,536,423 DUAL FLUID CIRCULATORY SUPPORT SYSTEM Thomas C. Robinson, West Newton, Mass., assignor to Thermo Electron Corporation, Waltham, Mass., a corporation of Delaware Filed Feb. 6, 1969, Ser. No. 797,094 Int. Cl. F04b 17/00 US. Cl. 417-394 Claims ABSTRACT OF THE DISCLOSURE A supplementary blood circulation system comprising an implantable diaphragm type blood pump actuated by a sealed charge of isotonic pumping fluid exchanged between two interconnected expansible chambers under the control of a hydraulic motor supplied with hydraulic actuating fluid under the control of signals from the natural circulatory system. Mechanical energy for actuating the blood pump control motor is stored in a reservoir of fluid under pressure by a pump actuated by a heat engine. The engine is operated by a nuclear-powered reservoir of thermal energy. The fluid supply for the motor is recirculated in a closed cycle and serves as the working fluid for the engine, as the lubricant for the system, and as a heat transfer medium for dissipating excess heat into the isotonic pumping fluid, through which it is dissipated into the blood stream.

My invention relates to prosthetic devices, and particularly to a novel implantable blood flow control system for supplementing the mammalian heart function.

In the correction and treatment of many physical disorders, it may be necessary to compensate for failure or weakness of the normal heart function over a substantial period of time. One approach that has been proposed is to excise the natural heart and replace it with a mechanical substitute that will perform its function. That approach naturally involves a highly traumatic surgical procedure with an attendant high mortality rate. Where some functional heart capacity can be expected to be retained, a preferred approach would be to supplement the natural heart function with a pump connected either in series or in parallel with the natural heart. One such device that has been developed is an implantable assist pump that is pneumatically actuated by an external source of energy supplied over air lines transcutaneously connected to the pump. The assist pump preferably is connected between the left ventricle and the aorta of the host; the left ventricle is preferred, because that organ normally does approximately 83 percent of the work performed by the heart on the blood. Obviously, it would be highly desirable to avoid the necessity for maintaining a transcutaneous energy supply to a pump of this type. Another inherent difficulty with such a system is that is has formerly been necessary to make electrocardiographic connections to the host, to provide control signals for synchronizing the air supply of the pump with the natural heart. It is the object of my invention to facilitate supplementing the action of a natural heart with some functional capability without external fluid and electrical connections to the host.

Briefly, the above and other objects of my invention are attained by a novel circulatory assist system of my invention, comprising three components which, with their interconnections, may be totally implanted in the body of the host. The first component consists of a hydraulically actuated 'blood pump that is implanted in the thoracic cavity and is connected between the left ventricle and the aorta. The second component is a power supply which, in its relation to the system, consists of a source of fluid Patented Oct. 27,1970

ice

under a first pressure for actuating the assist pump during its systolic phase, and a fluid sink at a lower pressure for receiving fluid from the assist pump during the systolic phase of the natural heart. The third component of the system is connected between the blood pump and the power supply and comprises means responsive to the ventricular pressure of the host for controlling the admission of fluid to, and the exit of fluid from, the pump in synchronism with the systolic phase of the natural heart. The blood pump control mechanism may be mechanically combined and implanted with the power supply, or it may be separately implanted, as under the left hemi-diaphragm. It is preferred not to combine it mechanically with the blood pump, as a blood pump of adequate size normally takes substantially all of the space that is usually available in the thoracic cavity.

The circulatory assist system of my invention supplies pumping energy as demanded by the host, in a manner that will be explained in detail below. In order to supply this energy most efficiently, I prefer to employ a fourstage system in which the primary source of energy is a radioactive substance that essentially radiates energy at a constant rate. This energy is absorbed in a thermal reservoir that preferably comprises a two-phase constant temperature system having a substantial latent heat of transition between one phase and the other. This thermal energy source is employed to heat the working fluid of a heat engine. The engine drives a pump to supply the hydraulic fluid from a low pressure reservoir that receives exhaust fluid from the actuator to a high pressure reservoir serving to supply pumping fluid to the actuator. The necessity for providing absolute seals between moving parts is, for the most part, avoided, and the construction of the apparatus is considerably simplified, by using the working fluid for the heat engine as the hydraulic pumping fluid, in a closed cycle, and by transferring waste heat from this fluid to the blood through the diaphragm in the blood pump by intermediate isotonic fluid means to be described. The discharge of waste heat in that manner produces a physiologically negligible temperaturerise in the blood stream, and yet maintains the exterior surfaces of the assist system at a substantially constant temperature for an indefinite period of time.

The manner in which the apparatus of my invention is constructed, and its mode of operation, will best be understood in the light of the following description, together with the accompanying drawings, of a preferred embodiment thereof.

In the drawings,

FIG. 1 is an orthogonal sketch, with parts omitted and parts broken away, of a heart assist power supply in accordance with my invention;

FIG. 2 is a cross-sectional elevation of the apparatus of FIG. 1, taken essentially along the lines 22 in FIG. 1, with parts omitted and parts broken away;

FIG. 3 is a schematic elevational sketch, with parts shown in cross-section, of a blood pump and blood pump control unit adapted to cooperate with the power supply of FIGS. 1 and 2;

FIGS. 3A and 3B are diagrammatic sketches of a piston and cylinder forming a part of the apparatus of FIG. 3, showing the parts in different relative position at different stages in an operating cycle;

FIG. 4 is a schematic cross-sectional view, taken essentially along the lines 4-4 in FIG. 3, showing the relationship between the diaphragm and the housing of the blood pump;

FIG. 5 is a schematic piping diagram of the blood assist system of my invention;

FIG. 6 is an elevational view, in cross-section, of the engine and fly wheel forming a part of the apparatus of FIG. 2;

FIG. 7 is a partly schematic rear view of the engine of FIGS. 2 and 6, with parts shown in cross-section, parts broken away and parts omitted, the apparatus being shown as seen from the right in FIGS. 2 and 6 and the portion in the section corresponding approximately to that indicated by the lines 777 in FIG. 6; and

FIG. 8 is a schematic elevational view of a pump suitable for use as the feedwater pump and the sump pump in the apparatus of FIG. 7 and elsewhere.

Referring first to FIG. 1, the pump power supply of my invention is enclosed in a suitable hermetically sealed container here shown as a cylinder having side walls 1 and end walls such as 3. This cylindrical housing may be made of stainless steel or the like, and is preferably provided on its outer surface with a biologically compatible coating of any suitable type conventionally used for that purpose. The housing 1 is provided with a single outlet through which pass two hydraulic lines 7 and 9, through a suitable seal 11. These conduits are preferably made of flexible tubing. As will appear, the conduit 7 serves to convey fluid under pressure to the blood pump control unit, to be described, and the conduit 9 serves to return fluid under lower pressure to the power supply at a lower temperature than the high pressure fluid supplied by the conduit 7.

Referring to FIGS. 1 and 2, the space within the outer housing not occupied by the power supply components is evacuated, and those components are insulated by foil insulation, shown schematically at 16. The insulation 16 comprises a number of layers of metal foil of tungsten, nickel, tantalum, molybdenum, or the like, with thoria or yttria powder between the foil layers to keep them approximately 2 mils apart. We have found this vacuum foil insulation to be highly eflicient in shielding the outer casing of the power supply from the extremely high temperatures inside the thermal energy storage compartment, to be described.

Considering next FIG. 3, the conduits 7 and 9 are connected to inlet fittings 13 and 15, respectively of a blood pump control unit generally designated 17. The blood pump control unit has an outlet fitting 19 connected through a tube 21 to an inlet fitting 23 on a left ventricle assist pump generally designated 25.

The assist pump 25 is provided with an inlet tube 27 adapted to be secured to the left ventricle by means of a conventional suture ring 29. -An outlet tube 31 is adapted to be grafted to the aorta by means of a conventional graft connection 32.

As shown in FIGS. 3 and 4, the assist pump 25 is provided with an outer housing 35, of stainless steel or the like, preferably having an exterior coating that will promote some tissue ingrowth for anchoring or positioning the pump such as a Dacron velour glued to the pump body.

Within the outer housing 35 is a pump diaphragm 37 preferably of a relatively thin polyurethane resin; i.e., approximately 0.03 inch in thickness. The inner surface 39 of this membrane 37 is preferably provided with a flocked Dacron surface which after implantation anchors a blood compatible pseudo-endothelium lining.

Before describing the elements of the system in further detail, its general operation will be considered. Basically, the power supply of FIG. 1 serves to supply fluid under pressure through the conduit 7 to the blood pump control unit 17 in FIG. 3. Fluid from the conduit 7 causes downward movement of a piston 41 in a cylinder 43 forming part of the blood pump control unit 17. The piston 41 is connected to one end of a metal bellows 42 that is connected at the other end to the end wall of the cylinder 43 to form an expansible chamber 44. The expansible chamber 44, the line 21 and the space between the housing 35 and the diaphragm 37 form a sealed container of constant volume for a fixed charge of pumping fluid. The latter is preferably a sterile, aqueous Saline solution,

to minimize shock in the event of leakage into the bloodstream.

When the piston 41 is moved downwardly in FIG. 3, hydraulic fluid 45 is forced into the space between the housing 35 and the diaphragm 37 of the blood pump to express blood under pressure to the aorta. When the piston nears the bottom of its stroke, the pressure above it is relieved, in a manner to be described, and the apparatus then awaits the next systolic contraction of the natural heart, whereupon the diaphragm 37 will be expanded and filed with blood and the piston 41 will rise to the position shown in FIG. 3.

At the end of the systolic contraction of the heart, the pressure inside the diaphragm will drop slightly below the pressure outside. That pressure drop is sensed by the blood control unit 17, triggering the next systolic phase of the blood pump substantially in synchronism with the natural dialstole. During the pumping process, the portion of the fixed charge of hydraulic fluid supplied from the expansible chamber 14 to the blood pump exchanges heat with the blood through the relatively thin diaphragm 37. The fluid in the chamber 44 is in thermal contact with the fluid in the return conduit 9 by conductive connections through the metal walls of the piston 41 and the bellows 42. The fluid in the line 9 is thus returned to the power supply at a slightly reduced temperature sufficient to make the equilibrium temperature of the fluid in the line 7 substantially constant.

The internal construction of the power supply of my invention will next be described. Referring first to FIG. 2, the apparatus includes a primary energy source 47 which is preferably a radioactive substance such as plutonium 238 nitride. The presently preferred amount of plutonium nitride is that suflicient to produce approximately 20 to 25 watts of power.

The plutonium nitride 47 is enclosed in a shield 49 that preferably comprises 6 millimeters of tantalum having an initial impurity of 1 part per million of plutonium 236. That amount of shielding is sufficient to keep the gamma dose rate equal to or less than the neutrol dose rate for a period of 5 years.

The shielded fuel capsule is enclosed in a container 51 of any suitable encapulating material such as Haynes 25 stainless steel. A vacant space 53, equal in volume to the isotope 47 is provided in the capsule 51 to allow for helium buildup during radioactive decay of the isotope 47. The container 35 serves the purpose of containing the highly toxic radioactive fuel, and the helium gas produced by alpha decay of the fuel, and providing incidental radiation shielding.

The fuel capsule 51 is enclosed within an energy storage chamber formed by a cylinder 55 attached to and formed integrally with a circular end wall 57 of stainless steel or the like. The chamber containing the capsule 51 is closed by a circular end wall 59, also of stainless steel. The fuel container is surrounded by an annular chamber formed outside the cylinder 55 and enclosed by the end Wall 57 and a cover 61, of stainless steel or the like.

Within the annular chamber is a toroidal ring 63 of thermal energy storage material. A presently preferred material for this purpose is the eutectic composition of 30 mole percent LiCl and 70 mol percent LiF. That material has a relatively high latent heat of fusion of 362 calories per cubic centimeter, and a convenient melting point of 930 F. It is stable, compatible with 304 stainless steel, and does not present a hydrogen release problem.

Heat energy stored in the thermal storage material 63 is supplied to the working fluid of a heat engine by means of a boiler comprising a coil wound about the periphery of the cover 61 of the thermal reservoir. While various compositions could be employed as the working fluid, water is presently preferred because it is highly stable, it has an eflicient working cycle, and its thermos dynamic properties are known with such precision as to greatly facilitate accurate design calculations.

High temperature, high pressure working fluid, preferably steam at a pressure of about 800 p.s.i.a. and a temperature of 900 F., is supplied from the boiler to the intake conduit 67 of a steam engine generally designated 69 and to be described in more detail below. The steam engine 69 drives a flywheel generally designated 71 to provide short term energy storage for mechanical damping and speed control, as will appear.

Before describing the internal construction of the power supply in further detail, its general operation will next be described in connection with the system block diagram of FIG. 5. I have there shown the blood pump control unit 17 quite schematically in its relationship with the blood pump and the power supply.

As indicated in FIG. 5, the low pressure fluid line 9 is connected to an expansible low pressure reservoir 73 which expands to the volume dictated by the amount of fluid in the low pressure portion of the system at any given time. That amount of fluid will fluctuate as dictated by the demands upon the assist system by the host, and will be regulated in accordance with the demand on the engine to maintain system stability in a manner that will appear below.

Pressure in the low pressure reservoir 73 is established at a predetermined value of, for example, 15 p.s.i.a. by means of a conduit 75 connected to the output of a sump pump 77 and by reservoir compliance which equalizes internal and near-ambient external pressures. The outer side of the sump pump 77 is also connected with a conduit 79 to the intake of a hydraulic pump 81 that serves to supply working fluid over a conduit 83 to a high pressure reservoir 85. The reservoir 85 is maintained at a nominal pressure of, for example, p.s.i.a., as by a spring or the like; that pressure will fluctate somewhat in dependence on demand, as will appear. The high pressure reservoir supplies fluid to the conduit 7 for the purposes described above. A relief valve 87 is connected across the hydraulic pump 81 to dump fluid from the high pressure reservoir into the loW pressure reservoir should the pressure in the high pressure reservoir exceed the desired value.

Fluid from the high pressure reservoir 85 is also supplied to the boiler 65 by means of a feed pump 91. Excess pressure in the outlet of the feed pump 91 is prevented by a relief valve 93 connected across the pump 91. As discussed above, working fluid from the boiler 65 is supplied to the engine 69 over the conduit 67. Exhaust fluid from the engine 69 is supplied to a condenser 95 through an exhaust line 97. As indicated schematically in FIG. 5, the condenser 95 is located in the high pressure reservoir 85, and the liquid in the high pressure reservoir serves as the coolant. Excess heat thus added to the liquid in the high pressure reservoir is removed in the pump 25, as generally described above.

The condenser 95 is preferably made in a manner known per se from small bore tubing, to which a tapered inlet passage is provided (as schematically shown in FIG. 7) so that the condenser will function properly regardless of the orientation of the host in a gravitational field. The outlet side of the condenser 95 is connected to the input side of the sump pump 77 over a line 99. The pressure in this line, at the input side of the sump pump, is the lowest in the system, and serves as a system sump for fluid leakage throughout the system. Such leakage is not only permitted, because it does no harm in this particular system, but is intentionally provided for to the extent necessary to provide lubrication of the working parts.

The details of the construction of the engine in FIG. 1 and associated hydraulic components will next be described. Referring to FIGS. 6 and 7, the engine comprises a head generally designated 101 connected to the intake pipe 67 and serving as an intake manifold. A poppet valve 103 is located in a guide cage 105 formed integral with the cylinder head 107 and provided with vents 108 serving to admit working fluid to the cylinder 111 when the valve 103 is raised. The cylinder 111 is preferably made of titanium, reinforced with a single coil of glass filament 113 so wound about the cylinder 111 that the individual turns of the filament are not in contact with each other.

In the cylinder is slidably mounted a piston generally designated by 115 and provided with an elongated skirt 117. The skirt 117 is slotted as indicated at 119 to admit a pair of stops 121 fixed in the wall of the cylinder. In the position of the piston shown, the stops 21 engage a striker plate 123 secured to an exhaust valve 125 to force it to the position shown in FIG. 6.

The piston is shown at bottom dead center. When it raises from that position, a spring 127 holds the valve 125 open until the latter strikes the poppet valve 103 to knock it up and admit a new slug of working fluid into the cylinder, thereby forcing the valve 125 closed and causing the piston to descend on the next working stroke.

The skirt 117 of the piston 115 is connected to a composite expansion seal connecting rod comprising an outer tube 129 and an inner tube 131 connected together and to an upper cap 133. The tube 131 is connected at its lower end to an end wall 135 of the skirt 137 of a piston generally designated 139 forming a part of the hydraulic pump 81.

The piston 139 is slidable in a cylinder 141. The head of the cylinder 141 is formed with an inlet port 143 and an outlet port 145, both shown in FIG. 7, for cooperation with a pair of check valves in a manner to be described below. The piston 139 is connected to a piston rod 147 journalled on a wrist pin 149 by means of an intermediate bearing 151. The pin 149 is located in a liner 153 forming part of the piston, as shown.

The piston rod 147 drives a crank shaft 155 having a crank arm 157 provided with a crank pin 159 journalled to the piston rod through an intermediate bearing 161. An eccentric 163 is fixed to the crank arm 157 to actuate the sump pump 77 and the feed pump 91 in a manner to be described below.

The crank shaft is journalled in a bearing 165 held in a support 167, the latter being fastened to a supporting cylinder 169 formed integral with the cylinder 141 of the pump 81. As shown in FIG. 6, the flywheel 171 is fixed on the crank shaft 155 for rotation within an inner housing 173 fixed to the support 169 and an outer housing 175 serving as a support connecting the cylinder 111 to the side wall 1 of the power supply 1.

Referring particularly to FIG. 7, the sump pump 77 and the feedwater pump 91 are mounted on the crank case walls 179 and 181, respectively, of the engine. The pump 77 has an actuator shaft 183 adapted to be reciprocated by the eccentric 163, and the feedwater pump 91 has an actuating shaft 185 likewise adapted to be reciprocated by the eccentric 163.

Referring to FIG. 8, the construction of the pump 91 is shown. The same construction may be employed for the pump 77. As shown in FIG. 8, the actuator shaft 185 is formed integral with a plunger 187 normally held in the position shown by a spring 189. When the plunger 187 is moved to the left in FIG. 8, an exhaust valve 191 will be held in the open position shown, whereas an intake valve 193 will be held in its closed position, as shown, during the same stroke. On the return stroke of the shaft 185, the intake valve will be opened and the exhaust valve closed in a manner that will be familiar to those skilled in the art. The check valves 82 and 84 for the pump 81 (see FIG. 7) may be of the same construction as those shown in FIG. 8. The bearings such as 195 for the pumps are preferably of graphite, and are lubricated by the water comprising the working fluid in the system.

Comparing FIGS. 7 and 8, it will be apparent that in view of the high pressure in the pumps 91 and 81 with respect to the low pressure existing in the condenser re- 7 turn line 99 at the inlet of the sump pump 97, net leakage will be into the sump pump. Leakage will thus be returned to the low pressure reservoir 73 by the sump pump. As indicated in FIG. 7, a conventional filter 197 is preferably installed at the outlet of the sump pump to catch any foreign matter that may accumulate.

The operation of the power supply will next be described in terms of its response to changes in the demand for pumping energy by the blood pump control unit 17.

Referring first to FIG. 2, the isotope 47 may be assumed to radiate energy at a constant rate. Variations in demands for heat energy from the thermal storage cell 63 are compensated for by the phase change of portions of the thermal energy storage material from solid to liquid or liquid to solid at constant temperatures- Referring now to FIGS. 5, 6 and 7, increased demands for pumping energy by the blood pump control unit result in a reduced pressure in the high pressure reservoir 85. The engine 69 does a constant amount of work per stroke. Some of this work is delivered to the sump pump 77 and the feedwater pump 91. However, the flow through these pumps, which is essentially the same and is determined by the flow rate of working fluid required by the engine, is only about one five-thousandths of the flow rate through the hydraulic pump 81. Accordingly, substantially all of the work done by the engine on each stroke is either delivered to the pump 81, or is absorbed by the flywheel. When the pressure in the high pressure reservoir 85 is reduced, the work done by the pump 81 per stroke is correspondingly reduced. The net difference between the work done on the pump and the energy delivered by the engine is transmitted to the flywheel, causing it to increase in speed. Accordingly, the engine speed will increase to maintain the desired flow of energy into the blood pump control unit. When the demand for pumping energy decreases, as when the host is resting, pressure in the high pressure reservoir 85 will increase, and the pump 81 will therefore absorb more energy per stroke. Since the amount available per stroke of the engine is fixed, the necessary energy will come partly from the flywheel, which will slow down to cause the engine to decrease in speed until the pressure in the high pressure reservoir 85 returns to the normal value. The response of the system can be tailored by selecting the flywheel inertia, the pressure drop across the hydraulic accumulator comprising the reservoirs 85 and 73, and the total volume of the high pressure reservoir 85. The latter factor determines the relative etfect of changes in the demand of the blood pump control unit 17 in terms of volume per stroke. Specifically, reducing the total volume of fluid in the system will increase the sensitivity of the engine speed to changes in demand, and vice versa.

Referring next to FIG. 3, the details of the blood pump control unit 17 will next be described. The apparatus comprises a housing generally designated 201, of metal or the like, divided and connected together in any convenient way, not shown, to facilitate assembly, and including the moving parts and passages which together function to control the supply of pumping energy to the blood pump. The main pump piston 41 is connected to and formed integrally with a smaller drive piston 203 slidable within a cylindrical bore 205 formed in the housing 201. The relatively high pressure in the high pressure line 7 is thus divided to a suitable lower value for communication with the blood pump.

In the position of the parts shown in FIG. 3, the upper portion of the spool valve 207 communicates with the exhaust line 9 through a passage 211, a passage 113, a reduced portion 215 formed on the piston 203, a passage 217, and by way of a restricted orifice 219 in parallel with the check valve 221. At the same time, the top of the piston 203 communicates with the high pressure supply line 7 through a passage 223, a reduced portion 225 formed on a spool valve 207, and a passage 227.

The spool valve 207 is resiliently urged to the position shown in FIG. 3 by means of a spring 224. The cylinder 209 below the spool valve 207 is in communication with the return line 9 by way of a passage 231. The space in the cylinder 43 outside of the expansible chamber 44 formed by the piston 41 and the bellows 42 is also in communication with the supply line, by way of a passage 233.

The spool valve 207 has a second operative position in which it engages a ledge 235 formed at the bottom of the cylinder 209. In this second position of the spool valve 207, the space above the piston 203 communicates with the return line 9 by way of a passage 237, a reduced portion 239 formed on the spool valve 207, a passage 241, and the restricted orifice 219 in parallel with the check valve 221.

The piston 203 operates over a range including three functionally different positions, The first is that shown in FIG. 3, in which the top of the spool valve 207 communicates with the return line 9 as described above. The second position is diagrammatically shown in FIG. 3A and corresponds to a lower position of the piston 203 in the cylinder 205 as shown in FIG. 3. In the posi tion shown in FIG. 3A, the passage 213 is closed. In that position, the passage 213- is closed by the top portion of the piston 35, and a passage 243 is closed by the lower portion of the piston 35. Thus, over a range of travel of the piston in which both the ports 213 and 243 are closed, the fluid above the spool valve 207 is trapped and the valve is locked in whatever position it may be at that time.

A third position of the piston 35 is illustrated in FIG. 3B. In that position, the reduced portion 215 on the piston 35 connects the passage 243 to a passage 245 that is directly connected to the high pressure supply line 7, for purposes to appear.

Operation of the blood pump control unit 17 will next be described, on the assumption that the parts have just reached the position shown in FIG. 3. In that position, with the high pressure line 7 in communication with the piston 203, the piston 41 will be driven downwardly to pump fluid from the expansible chamber 44 through the conduit 21 into the blood pump 25. The bladder 37 in the blood pump will be compressed, causing a check valve 251 in the blood pump to close as shown in the drawings and causing a check valve 253 to open and admit blood expressed from the bladder to the aorta. In the pumping process, the fluid driven by the piston 41 into the chamber between the housing 35 and the bladder 37 of the blood pump 25 will be thoroughly mixed, facilitating heat exchange between that fluid and the blood within the bladder 37.

As the piston 203 moves downwardly, the passage 213 will be closed by the top part of the piston. As illustrated in FIG. 3A, the fluid over the spool valve 207 will be trapped, locking the valve in position.

When the piston 203 moves down far enough so that the reduced portion 215 formed on it will connect the passages 243 and 245, high pressure fluid will be admitted above the valve 207 to move it down against the spring 229 until it engages the stop ledge 215. The passage 237 above the piston 203 will be now returned to the line 9 over the reduced portion 239 on the spool valve 207, the passage 247, and through the reduced orifice 219.

The apparatus will remain in the position just described, with the piston 41 down and in the position shown in FIG. 3B, and with the spool valve 207 down and held down by high pressure fluid, until the next systolic contraction of the natural ventricle. When that occurs, blood under ventricular pressure will enter the tube 207 and open the valve 251. The valve 253 will be closed, and the diaphragm 37 will be expanded to drive pumping fluid up into the expandible chamber 44, raising the piston 41. As the piston 41 moves upwardly, the passage 243 will be closed and the valve 207 will remain locked in its lower position by the trapped fluid above it. The fluid above the piston 203 will be pumped out into the reduced orifice 219, relieved as the pressure reaches a predetermined level by the opening of the check valve 221, and thereby producing a pressure across the orifice 219 high enough for the purpose next to be described, but low enough that it will not tax the natural ventricle when reflected back as a lower pressure in the chamber 44.

When the piston 203 rises sufi'iciently to connect the passages 213 and 215 in FIG. 3, the pressure above the spool valve 207 will fall to that established by the drop across the orifice 219 described above. The piston will continue to rise, until, toward the end of the natural systole, the ventricular pressure will drop. That drop in pressure will allow the spring 229 to move the spool valve 207 back to the position shown in FIG. 1, with the result that the pumping stroke first described above will be repeated, driving blood to the aorta in an amount equal in volume to the volume of blood taken into the blood pump 25 during the previous ventricular systole. It will be apparent that the lower position of the piston 41 is determined by the position of the piston 203 at which the passages 243 and 245 in FIG. 3 are opened, whereas the upper position of the piston 41 will be determined by the point during the natural systole at which the ventricular pressure drops. By that arrangement, the volume of blood delivered at each stroke is determined by the physiological control system as determined by the varying needs of the host, and the timing of each stroke is also determined by the host and is transmitted to the blood pump control unit as the signal comprising the ventricular pressure drop towards the end of the systole. Thus, the assist pump acts to reduce the demand on the natural heart without interfering with the operation of the circulatory system of the host.

It will be apparent that the power supply fluid outside of the piston 41 and the bellows 42 will exchange heat with the tropped isotonic pumping fluid inside the piston and bellows, thereby lowering the temperature in the return line 9 with respect to the incoming temperature in the high pressure line 7. Suflicient heat can be exchanged in this manner to maintain thermal equilibrium in the system without unduly heating the blood.

While I have described my invention with respect to the details of a preferred embodiment thereof, many changes and variations will occur to those skilled in the art upon reading my description, and such can obviously be made without departing from the scope of my invention.

Having thus described my invention, what I claim is:

1. A circulatory assist system, comprising a first fluid reservoir, a second fluid reservoir, a first fluid circuit comprising said first reservoir, a boiler, a first pump connected between said first reservoir and said boiler to supply fluid from said reservoir to said boiler at a first pressure, a source of heat at constant temperature thermally connected to said boiler, a heat engine connected between said boiler and said condenser to be driven by heated fluid from said boiler, a second pump connected between said condenser and said second reservoir to supply condensate from said condenser to said second reservoir at a second pressure below said first pressure, a third pump connected between said second reservoir and said first reservoir to supply fluid from said second reservoir to said first reservoir at a third pressure between said first and second pressures, means controlled by said engine for driving said pumps, an implantable heart assist pump having an expandible blood chamber and a pumping fluid chamber separated from the blood chamber by a flexible diaphragm, a fluid motor connected between said reservoirs and comprising a pressure responsive variable volume fluid chamber connected to said pumping fluid chamber, and control means responsive to the pressure in said blood chamber to actuate said motor to alternately admit fluid from said first reservoir to said pressure responsive chamber to drive pumping fluid into said blood pump and then discharge the admitted fluid to said second reservoir and thereby actuate the blood pump.

2. In a circulatory assist system, a closed cycle fluid energy exchange system comprising a high pressure liquid reservoir, a low pressure liquid reservoir, a liquid actuated implantable blood pump, liquid motor means having a working chamber connected to said pump and liquid operating connections to said reservoirs to supply working liquid to said pump by absorbing energy from liquid from said high pressure reservoir and returning it at reduced pressure to said low pressure reservoir, said motor means comprising relatively moving parts lubricated by leakage from said high pressure reservoir into said working chamber and from said working chamber into said low pressure reservoir, a source of heat at constant temperature, a boiler thermally connected to said source, a first pump connected between said high pressure reservoir and said boiler to supply liquid at a first pressure to be vaporized in said boiler, a condenser thermally connected to the liquid in said high pressure reservoir, a heat engine connected between said boiler and said condenser to extract work from the vapor from said boiler, a sump pump connected between said condenser and said low pressure reservoir to return condensate from said boiler to said low pressure reservoir at a second pressure below said first pressure, a hydraulic pump connected between said low pressure reservoir and said high pressure reservoir to return liquid in said low pressure reservoir to said high pressure reservoir at a third pressure between said first pressure and said second pressure, and means controlled by said engine for driving said pumps.

3. A fluid circulatory support system, comprising a source of heat at constant temperature, a boiler in thermal contact with said source, a first water reservoir, 2. second water reservoir, a condenser in said water reservoir, a feedwater pump connected between said first water reservoir and said boiler to supply water at a first pressure to said boiler, a hydraulic pump connected between said first and second reservoirs to supply water to said first reservoir at a second pressure below said first pressure, a sump pump connected between said condenserand said second reservoir to supply water to said second reservoir at a third pressure below said second pressure, a flywheel, a steam engine connected between said boiler and said condenser and having an output shaft connected to drive said flywheel and said pumps, an implantable fluid actuated blood assist pump, and water actuated blood pump control means connected between said blood pump and said reservoirs to actuate said blood pump.

4. A fluid circulatory support system, comprising first and second liquid reservoirs, a source of heat at constant temperature, pumping means connected between said reservoirs for supplying liquid from said reservoirs to said first reservoir at a first pressure, heat engine means connected between said source and said reservoirs by a working fluid circuit using liquid from said reservoirs, means connecting said engine to drive said pumping means, an implantable liquid actuated blood pump, and liquid actuated blood pump control means connected between said blood pump and said reservoirs to actuate said blood pump.

5. The apparatus of claim 4, in which said heat engine means and said pumping means comprise, in combination, a vapor cycle engine having an intake and an exhaust, a boiler thermally connected to said heat source, a liquid feed pump driven by said engine and connected between said first reservoir and said boiler, said boiler being connected between said feed pump and said intake, a condenser, and means connecting said condenser between said exhaust and said second reservoir.

6. The apparatus of claim 5, further comprising means 1 1 mounting said condenser in thermal contact with the liquid in said first reservoir.

7. The apparatus of claim 6, in which said source of heat comprises a charge of radioactive material, and a thermally energy storage cell of material melting at a constant temperature surrounding said radioactive material and in thermal contact with said boiler.

8. The apparatus of claim 6, in which said engine and said pump comprise relatively moving parts lubricated by leakage of said liquid.

9. The apparatus of claim 8, in which said reservoirs, said heat source, said heat engine means, and said pumping means are enclosed in an evacuated housing and insulated by layers of bright metal foil in said housing, said layers being separated by particles of metal oxide.

10. A circulatory support system, comprising a fluid diaphragm pump adapted to be connected in the circulatory system of a host to supplement the action of the natural heart, and a pumping fluid supply system connected to said pump, said pumping fluid supply system comprising an expansible chamber of hydraulic fluid connected to said pump to supply fluid under pressure to the pump when compressed by fluid under pressure applied to said chamber and to receive fluid from the pump when expanded, a supply reservoir of fluid under pressure, a return reservoir of fluid under a lower pressure, fluid motor means connected between said reservoirs and said expansible chamber for alternately connecting said supply reservoir to said chamber to compress it and connecting said return reservoir to said chamber, the pressure in said return reservoir being below the pressure in said chamber exerted by the diaphragm in said pump when exposed to ventricular systolic blood pressure, a pump connected between said reservoirs to pump fluid to said supply reservoir from said return reservoir, a heat engine connected to said pump to drive the pump when supplied with Working fluid, a source of energy, and means controlled by said source and connected between said reservoir and said engine to supply working fluid to said engine.

References Cited UNITED STATES PATENTS 2,815,715 12/1957 Tremblay 103-152 XR 3,434,162 3/1969 Wolfe 31 ROBERT M. WALKER, Primary Examiner US. Cl. X.R. 31 

